Pulse-echo radio velocity indicator



2 Sheets-Sheet l Filed April 25, 1944 INVENTOR. Evam HTTAIYEY @et I2,1948. J. EVANS PULSE-ECHO RADIO VELOCITY INDICATOR 2 Sheets-Sheet 2Filed April 25, 19%

a m m m may 1N VEN TOR.

I0 Ivan@ BY @Ef/I HTTO/YEY TES iran si' 2,456,946 PULSE-ECHO RADIOVELGCITY MDICATGR John Evans, Kingston, N. J., assigner to RadioCorporation oi America, a corporation of Dela- Application Apri! 25,i944, Serial No. 532,639 E 6 Claims. (Cl. SiS-8) 2 My invention relatesto radio locator systems reception by providing a transmit-receive orT-R and particularly to systems of the pulse-echo box i2 of conventionaldesign'. The function oi type. the T-R box I2 is to short or effectivelyto open, An object of the present invention is to prothe line to thereceiver during the transmission vide an improved method of 'and meansfor deter- 5 of a pulse. Separate antennas for transmission mining thespeed of a moving object. and reception may be employed, if preferred.

A further object of the invention is to provide Referring t the circuitfOr producing thePlllSeS the speed and directio object.

In a preferred embodiment of mitter is ma certain -frequenc quency beipulses.

At the receiver, the paire The amount of be indicated by measure of theof the pulse retowards its centered position. centering current, whichmay -current voltmeter, is a rate and direction of movement ectingobject.

The invention will be better understood from the following descriptiontaken in connection with the accompanying drawing in which Figure 1 is ablock and circuit diagram of one embodiment of the invention,

Figure 2 is a schematic view of the target electrode and mask of thecathode ray tube shown in Fig. 1,

Figure 3 is a block and d' erential detector circuit shown in Fig. 1,and

Figure 4 is a graph that is referred to in explaining the operation ofthe system shown in Fig. 1.

Referring to Fig. 1, a radio transmitter IG is pulse modulated by aperiodically recurring pair A and B which are amplitude modulated entfrequency rates F1 and F2, respec- The radiol pulses are radiated froman antenna l l which may also be utilized for pulse circuit diagram ofthe A and B, a sine wave oscillator i3, which osciland 100 cycles persecmodulate the carrier wave.

The pulses reected from the moving object are picked up by the antenna Hand supplied to a radio receiver 3i de ray tube 3 The cathode ray tube33 com 3d, a control grid 36,

under certain co after. The tube 33 als the conductors 43 to the taldeecting plates 42. A sawtooth deflecting voltage is applied over a pairof conductors 43 to the plate 42 from a sawtooth wave generator 44. Theconnection from the generator 44 to the conductors 43 may be throughcoupling capacitors 46 and 41. Synchronization of the sawtooth wavegenerator 44 with the pulse transmission may be maintained by supplyingthe pulses B over a conductor 48 to the generator 44.

The target electrode 38 is connected to an output conductor 49 whichsupplies electron beam current through one or the other of a pair oftuned iilter circuits and 52 to a differential detector circuit 53whenever the electron beam strikes the target 378. The filters 5| and 52are tuned to the frequencies Fi and F2, respectively, to pass currentsat these frequencies only. The differential detector circuit 53 (shownin detail in Fig. 3) supplies a direct-current voltage over deectingplates 42 for centering the electron beam. The amount and polarity ofthis centering current is indicated by a direct-current voltmeter 54whereby the rate and direction of motion of the pulse reflecting objectis indicated as explained below.

As shown in Fig. 3, the differential detector circuit 53 may comprisedetector tubes 58 and 51 having their control grids connected to thefilters 5| and 52, respectively. A direct-current operating voltage issupplied to the anodes of tubes 56 and 51 through anode resistors 58 and58, respectively. The anodes of the tubes 56 and 51 are connectedthrough the conductors 43 to the horizontal deflecting plates 42. Thedirect-current voltmeter 54 is connected between the anodes of thedetector tubes 56 and 51.

Since the amount of direct-current flow through the anode resistors 58and 59 depends upon the amount of signal applied to the control grids ofthe corresponding detector tubes, there will be a direct-currentcentering voltage applied through the conductors 43 to the deflectingplates 42 that depends on the said applied signal. This D.C. voltage ismeasured by the meter 54 to indicate the rate and direction of motion ofthe pulse reflecting object.

The operation of the system will be more clearly understood by referringto Fig. 2 where the cathode ray trace is represented by the broken line6l. Here it is assumed that the electron beam is deflected left to right(looking from the electron gun toward the target 38). In the absence ofa received pulse, the beam trace is below the masks 39 and 4| and thetarget 38. Upon the the beam is deected upwardly and held there for theduration of the pulse. Thus the beam trace produced by pulses A and Bisl indicated at A' and B.

If the pulse traces A' and B' are centered with between the masks 38 and4I, no beam electrons strike the target 38 and no current is suppliedover the conductor 49. If, however, the traces A' and B' are oi centeras illustrated in Fig. 2, the beam is deflected upwardly onto the target38 by one of the pulses (by pulse A in the example shown). Since therecurring A pulses are amplitude modulated, the result of the off-centercondition illustrated will be that the electron beam will strike thetarget 38 during a high amplitude modulation period or instant of the Apulses but will fail to strike it or will strike it for a shorter timeduring the low amplitude modulation period or instant. Thus, a currentwhich varies at the modulation frequency F1 appears in the conductor 49,passes through the filter 5l (but not through lter 52) and causes adecrease (or increase depending upon the type of detector) in the D.C.anode current of detector 58. Any alternating current in the detectortube outputs is filtered out by the bypass capacitors 64 and 66. Theresulting D.C. differential voltage on the conductors 43 substantiallycenters the traces A and B' and holds them centered, only enough of theright hand edge oi the trace A striking the target to maintain thiscondition. The faster the reilecting object is moving. the greater isthe amount of centering voltage required to maintain the centeredcondition, and. the greater is the deection oi the meter I4. Thus themeter 64 may be calibrated to indicate directly the speed of thereflecting object.

If the reiiecting object is moving in the opposite direction, thereverse centering action takes place, that is, the trace B' now strikesthe target 38, current passes through the filter 62 only, and acentering voltage of reversed polarity is applied through the conductors43 to the horizontal deecting plates 42. The reading of the meter 64 isnow reversed with respect to the previous reading and the value of thereading indicates its speed.

The above described centering action of the diierential detector circuitis illustrated in Fig. 4 where the graph 66 illustrates how thecentering voltage changes at the anode of tube 58 for different speedsof a reflecting object travelling in one direction, and where the graph61 illustrates how the centering Voltage changes at the anode of thetube 51 in the case where the object is travelling in the oppositedirection.

It will be apparent that the invention is not limited to the specificcircuit illustrated. For example, the output of the receiver 3| may beapplied to the control grid 36 of the cathode ray tube instead of to thevertical deflecting plates 32. Then with the electron gun biased toelectron beam cut-oi in the absence of a received pulse, and with thebeam positioned to sweep across the masks 39 and 4l and the target 38,the beam electrons will strike the target 38 during the reception ofeither the pulse A or the pulse B if the reecting object is moving.Thus, the centering action is the same as in the example illustrated.

I claim as my invention:

1. In a system wherein there is a cathode ray tube having means forproducing an electron beam, the method of determining the speed of amoving object which comprises producing regularly recurring radiopulses, transmitting said pulses toward said object, receiving saidpulses after reiiection, modulating said electron beam by said receivedpulses while sweeping it along a time axis in synchronism with the pulsetransmission, utilizing the electrons of said beam during the electronbeam modulation by said pulses to center the beam trace of said pulseson said time axis, and indicating the resulting amount of centeringcontrol whereby the rate of motion `of said object is indicated.

2. In a system for determining the speed of a moving object, means forproducing regularly recurring radio pulses, means for transmitting saidpulses toward said object, means for receivi-ng said pulses afterreflection, a cathode ray tube and means -for producing an electron beamtherein, means for sweeping said beam along a time axis in synchronismwith the pulse transmission, means for modulating said beam by saidreceived pulses, means comprising a target electrode in said cathode raytube for utilizing the electrons of said beam during the electron beammodulation by said pulses to produce a centering voltage, means fordeecting said fbeam :by said centering voltage to center the beam onsaid time axis, and means for indicating the resulting amount ofcentering voltage whereby the rate Iof mot-ion of said object isindicated.

3. The method of determining the speed of a moving objectl which-comprises producing regularly recurring pairs of radio pulses,modulating each of the pulses of said-pair at a diierent frequency,transmitting said pulses toward said object, receiving said pulses afterreflection, modu lating an electron beam by said received pulses whilesweeping it along a time axis in synchronism with the pulseltransmission, utilizingthe electrons of said Ibeam during the electronbeam modulation by one of the pulses in said pair to center the beamtrace of said reneoted pair of pulses on said time axis, and indicatingthe resulting amount of centering control whereby the rate of moti-on of'said object is indicated.

4. The method o f determining the speed of a moving object whichcomprises producing regubeam by one of the pulses in said pair to centerthe beam trace of said rellected pair of pulses on said time axis, andindicatingv the resul-ting amount of centering control whereby the rateof motion of said object is indicated.

5. In a system for determining the speed 'of a movingv object, means forproducing regularly pulses, means for modulating each of the pulses ofsaid pair at a different frequency, means forv transmitting said pulsestoward sai-d object, means for receiving said pulses deilection of theelectron after reection from said object, a cathode ray tube and meansfor producing an electron beam therein, means for sweeping said beamalong a time axis in synchronism with the pulse transmoving object,means for.

mission, means for modulating said beam by said received pulses, meanscomprising a target electrode in said cathode ray tube which ispositioned to be struck by the electrons of said beam during themodulation thereof by one of the pulses in said pair for producing acentering voltage, means for deiiecting said .beam along said time axisby said centering voltage to--center the ibeam trace of said reiiectedpair of pulses on said time axis, and means for indicating the resultingamount of centering voltage whereby the rate of motion of said object isindi-cated.

6. In a system for determining the speed of a producing regularlyrecurring pairs of radio pulses, means for modulating each of the pulsesof said pair at a diierent l frequency rate, means for transmitting saidpulses toward said object, means for receiving said pulses afterreflection from said object, a cathode ray tube and means for producingan electron -beam therein, means for sweeping said lbeam along a timeaxis in synchronism with the pulse transmission, means for modulatingsaid beam by said received pulses to producetwo pulse traces, a targetelectrode in said cathode ray tube, centering circui-t :means forcentering said traces with respect to said target, said target beingpositioned so that it is struck by one or the other of said pulse tracesin response to said traces getting off center, means for deflecting saidbeam by the output of said centering circuit to center the two .pulseltra-ces wit-h respect to said target in response to said traces gettingonv center, and means for indicating the resulting centering circuitoutput whereby the rate of motion of said object is indicated.

JOHN EVANS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

